Shaped Pulses for Selective Inversion in Solid-State Deuteron NMR Spectroscopy

Abstract

Double sideband modulation and pulse shaping can be combined to improve the performance of selective pulses in solid-state deuteron NMR. Efficient off-resonance selective inversion of deuterons requires simultaneous irradiation of both spin-1 transitions, i.e., at symmetric offsets from the Larmor frequency (ν₀± Δ). This is best accomplished with double-sideband-modulated pulses. Frequency-selective profiles can be improved by shaping the RF pulses. A variety of commonly used selective pulse shapes are evaluated for their applicability to solid-state deuteron powder patterns. A new pulse shape is introduced; the squared isosceles triangle. Generally, pulses with low bandwidth–duration product, such as the Gaussian envelope, are found to be the most effective for selective inversion in solid-state²H NMR. This is a consequence of the large inhomogeneous quadrupolar interaction and fast, anisotropic spin–spin relaxation.